Internet Engineering Task Force MMUSIC WG
Internet Draft Y. Nomura
Fujitsu Labs.
R. Walsh
J-P. Luoma
Nokia
H. Asaeda
INRIA
H. Schulzrinne
Columbia University
draft-ietf-mmusic-img-framework-07.txt
June 21, 2004
Expires: December 2004
A Framework for the Usage of Internet Media Guides
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Abstract
This document defines a framework for the delivery of Internet Media
Guides (IMGs). An IMG is a structured collection of multimedia
session descriptions expressed using SDP, SDPng or some similar
session description format. This document describes a generalized
model for IMG delivery mechanisms, the use of existing protocols and
the need for additional work to create an IMG delivery
infrastructure.
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resources including web pages. IMGs provide an envelope for metadata
formats and session descriptions defined elsewhere with the aim of
facilitating structuring, versioning, referencing, distributing, and
maintaining (caching, updating) such information.
IMG metadata may be delivered to a potentially large audience, who
use it to join a subset of the sessions described, and who may need
to be notified of changes to the IMG metadata. Hence, a framework for
distributing IMG metadata in various different ways is needed to
accommodate the needs of different audiences: For traditional
broadcast-style scenarios, multicast-based (push) distribution of IMG
metadata needs to be supported. Where no multicast is available,
unicast-based push is required too.
This document defines a common framework model for IMG delivery
mechanisms and their deployment in network entities. There are
three fundamental components in IMG framework model: data types,
operation sets and entities. These components specify a set of
framework guidelines for efficient delivery and description of IMG
metadata. The data types give generalized means to deliver and
manage the consistency of application-specific IMG metadata. IMG
operations cover traditional broadcast-style scenarios,
multicast-based distributions, unicast-based push and interactive
retrievals similar to web pages. Since we envision that any
Internet host can be a sender and receiver of IMG metadata, a host
involved in IMG operations performs one or more of the roles
defined as the entities in IMG framework model. These are then
shown in a number of simplified deployment scenarios. The
requirements for IMG delivery mechanisms and descriptions can be
found in the IMG requirements document [4].
Then, this document outlines the use of existing protocols to create
an IMG delivery infrastructure. It aims to organize existing
protocols into a common model and show their capabilities and
limitations from the viewpoint of IMG delivery functions. One of the
multicast-enabling IMG requirements is scaling well to a large number
of hosts and IMG senders in a network. Another issue is the need for
flexibility and diversity in delivery methods, whereas existing
protocols tend to be bound to a specific application.
2 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
Internet Media Guide (IMG): IMG is a generic term to describe
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the formation, delivery and use of IMG metadata. The
definition of the IMG is intentionally left imprecise. [4]
IMG Element: The smallest atomic element of metadata that can be
transmitted separately by IMG operations and referenced
individually from other IMG elements. [4]
IMG Metadata: A set of metadata consisting of one or more IMG
elements. IMG metadata describes the features of multimedia
content used to enable selection of and access to media
sessions containing content. For example, metadata may
consist of the URI, title, airtime, bandwidth needed, file
size, text summary, genre and access restrictions. [4]
IMG Description: A collection of IMG metadata which has a
relationship to other IMG metadata. There are three data
types to describe the relationship: Complete IMG
Descriptions, Delta IMG Description and IMG pointer.
IMG Delivery: The process of exchanging IMG metadata both in
terms of large scale and atomic data transfers. [4]
IMG Sender: An IMG sender is a logical entity that sends IMG
metadata to one or more IMG receivers. [4]
IMG Receiver: An IMG receiver is a logical entity that receives
IMG metadata from an IMG sender. [4]
IMG Transceiver: An IMG transceiver combines an IMG receiver and
sender. It may modify received IMG metadata or merge IMG
metadata received from a several different IMG senders. [4]
IMG Operation: An atomic operation of an IMG transport protocol,
used between IMG sender(s) and IMG receiver(s) for the
delivery of IMG metadata and for the control of IMG
sender(s)/receiver(s). [4]
IMG Transport Protocol: A protocol that transports IMG metadata
from an IMG sender to IMG receiver(s). [4]
IMG Transport Session: An association between an IMG sender and
one or more IMG receivers within the scope of an IMG
transport protocol. An IMG transport session involves a
time bound series of IMG transport protocol interactions
that provide delivery of IMG metadata from the IMG sender
to the IMG receiver(s). [4]
IMG Transfer: A transfer of IMG metadata consisting of Complete
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IMG Descriptions, Delta IMG Descriptions and/or IMG
Pointers.
3 IMG Common Framework Model
Two common elements are found in all of existing IMG candidate cases:
the need to describe the services; the need to deliver the
descriptions. In some cases, the descriptions are multicast enablers
(such as the session parameters of SDP) and are thus intrinsically
part of the delivery aspects, and in other cases descriptions are
application-specific (both machine and human readable). Thus, the
technologies can be roughly divided into three areas:
o Application-specific Metadata -- data describing the services'
content and media which are both specific to certain
applications and generally human readable.
o Delivery Descriptions -- the descriptions (metadata) that are
essential to enable (e.g. multicast) delivery. These include
framing (headers) for application-specific metadata, the
metadata element identification and structure, and fundamental
session data.
o Delivery Protocols -- the methods and protocols to exchange
descriptions between the senders and the receivers. An IMG
transport protocol consists of two functions: carrying IMG
metadata from an IMG sender to an IMG receiver and controlling
an IMG transport protocol. These functions are not always
exclusive, therefore some messages may combine control
messages and metadata carriage functions to reduce the amount
of the messaging.
3.1 IMG Data Types
A data model is needed to precisely define the terminology and
relationships between sets, supersets and subsets of metadata. A
precise data model is essential for the implementation of IMGs
although it is not within the scope of this framework and requires a
separate specification. However there are three IMG data types in
general: Complete IMG Descriptions, Delta IMG Descriptions and IMG
Pointers.
3.1.1 Complete IMG Description
A Complete IMG Description provides a complete syntax and semantics
to describe a set of metadata, which does not need any additional
information from any other IMG element.
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Note, this is not to be confused with "complete IMG metadata", which,
although vaguely defined here, represents the complete IMG metadata
database of an IMG sender (or related group of IMG senders --
potentially the complete Internet IMG knowledge). An IMG sender will
generally deliver only subsets of metadata from its complete database
in a particular IMG transport session.
3.1.2 Delta IMG Description
A Delta IMG Description provides only part of a Complete IMG
Description, defining the difference from a previous version of the
Complete IMG Description in question. Delta transfers may be used to
reduce network resource usage (it may be more bandwidth and
congestion friendly), for instance when data consistency is essential
and small and frequent changes occur to IMG elements. Thus, this
description itself cannot represent a complete metadata set until it
is combined with existing, or future, description knowledge.
3.1.3 IMG Pointer
An IMG Pointer provides a simple identifier or locator, such as a
URI, that the IMG receiver is able to reference (or reference and
locate) specific metadata with. This may be used to separately obtain
metadata (Complete or Delta IMG Descriptions) or perform another IMG
management function such as data expiry (and erasure). The IMG
Pointer may be used to reference IMG metadata elements within the IMG
transport session and across IMG transport sessions. This pointer
type does not include IMG metadata per se (although it may also
appear as a data field in Complete or Delta IMG descriptors).
3.2 Operation Set for IMG Delivery
A finite set of operations both meets the IMG requirements [4] and
fits the roles of existing protocols. These are crystallized in the
next few sections.
3.2.1 IMG ANNOUNCE
When an IMG receiver participates in unidirectional communications
(e.g. over satellite, terrestrial radio and wired multicast networks)
an IMG receiver may not need to send any IMG message to an IMG sender
prior to IMG metadata delivery. In this case, an IMG sender can
initiate unsolicited distribution for IMG metadata and an IMG sender
is the only entity which can maintain the distribution (this includes
scenarios with multiple and co-operative IMG senders). This operation
is useful when there are considerably large numbers of IMG receivers
or the IMG receiver(s) do not have a guaranteed uplink connection to
the IMG sender(s). The IMG sender may also include authentication
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data in the announce operation so that IMG receivers may check the
authenticity of the metadata. This operation is able to carry any of
the IMG data types.
Note, there is no restriction to prevent IMG ANNOUNCE from being used
in an asynchronous solicited manner, where a separate operation
(possibly out of band) enables IMG receivers to subscribe/register to
the IMG ANNOUNCE operation.
3.2.2 IMG QUERY
If an IMG receiver needs to obtain IMG metadata, an IMG receiver can
use an IMG QUERY operation and initiate a receiver-driven IMG
transport session. The IMG receiver expects a synchronous response to
the subsequent request from the IMG sender. This operation can be
used where a bi-directional transport network is available between
the IMG sender and receiver. Some IMG receivers may want to obtain
IMG metadata when a resource is available or just to avoid caching
unsolicited IMG metadata. The IMG receiver must indicate the extent
and data type of metadata wanted in some message in the operation
(extent indicates the number and grouping of metadata descriptions).
In some cases requesting an IMG sender's complete IMG metadata may be
feasible, in others it may not.
3.2.3 IMG RESOLVE
An IMG sender synchronously responds, and sends IMG metadata, to an
IMG QUERY which has been sent by an IMG receiver. This operation
can be used where a bi-directional transport network is available
between the IMG sender and receiver. If the IMG QUERY specifies a
subset of IMG metadata (extent and data type) that is available to
the IMG sender, the IMG sender can resolve the query; otherwise, it
should indicate that it is not able to resolve the query. The IMG
sender may authenticate the IMG receiver to investigate the IMG
QUERY operation in order to determine whether the IMG receiver is
authorized to be sent that metadata. The sender may also include
authentication data in the resolve operation so that IMG receivers
may check the authenticity of the metadata. This operation may
carry any of the IMG data types.
3.2.4 IMG SUBSCRIBE
If an IMG receiver wants to be notified when the IMG metadata it
holds is stale, the IMG receiver can use the IMG SUBSCRIBE operation
in advance in order to solicit notify messages from an IMG sender.
This operation may provide the IMG sender with specific details of
which metadata or notification services it is interested in (in the
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case where the IMG sender offers more than the simplest "all data"
service). This operation implicitly provides the functionality of
unsubscribing to inform an IMG sender that an IMG receiver wishes
to stop getting certain (or all) notifications. It should be noted
that unsubscription may be provided implicitly by the expiry
(timeout) of a subscription before it is renewed. However, these
details belong to a messaging protocol instantiation of this
operation are beyond the scope of this document.
Since the IMG receiver does not know when metadata will be updated
and the notify message will arrive, this operation does not
synchronize with the notify messages. The IMG receiver may wait for
notify messages for a long time. The IMG sender may authenticate the
IMG receiver to investigate whether an IMG SUBSCRIBE operation is
from an authorized IMG receiver.
3.2.5 IMG NOTIFY
An IMG NOTIFY is used asynchronously in response to an earlier IMG
SUBSCRIBE. An IMG NOTIFY operation generates a notify message
indicating that updated IMG metadata is available or part of the
existing IMG metadata is stale. An IMG NOTIFY may be delivered more
than once during the time an IMG SUBSCRIBE is active. This operation
may carry any of the IMG data types. The IMG sender may also include
authentication data in the IMG NOTIFY operation so that IMG receivers
may check the authenticity of the messages.
3.2.6 Binding Between IMG Operations and Data Types
There is a need to provide a binding between the various IMG
operations and IMG data types to allow management of each discrete
set of IMG metadata transferred using an IMG operation. This binding
must be independent of any particular metadata syntax used to
represent a set of IMG metadata, as well as be compatible with any
IMG transport protocol. The binding must uniquely identify the set of
IMG metadata delivered within an IMG transfer, regardless of the
metadata syntax used. The uniqueness may only be needed within the
domains the metadata is used but this must enable globally unique
identification to support Internet usage. Scope/domain specific
identifications should not 'leak' outside of the scope, and always
using globally unique identification (e.g. based on URIs) should
avoid this error.
The binding must provide versioning to the transferred IMG metadata
so that changes can be easily handled and stale data identified, and
give temporal validity of the transferred IMG metadata. It must
expire the IMG metadata by indicating an expiry time, and may
optionally provide a time (presumably in the future) from when the
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Some IMG metadata may be distributed to a large number of IMG
receivers. If, for example, some IMG metadata is public information
and the IMG sender provides the same information for all IMG
receivers. This kind of IMG metadata may be distributed from one IMG
sender to multiple IMG receivers (Figure 4) and/or or may be relayed
across a set of IMG transceivers that receive the IMG metadata,
possibly filter or modify its content, and then forward it.
+----------+ +----------+
| IMG | | IMG |
| Sender |---- ---->| Receiver |
+----------+ \ / +----------+
\ /
. \ +-----------+ / .
. -->|IMG |----- .
. -->|Transceiver| \ .
/ +-----------+ \
+----------+ / \ +----------+
| IMG | / ---->| IMG |
| Sender |---- | Receiver |
+----------+ +----------+
Figure 4: A Relay Network with an IMG Transceiver
IMG senders and receivers are logical functions and it is possible
for some or all hosts in a system to perform both roles, as, for
instance, in many-to-many communications or where a transceiver is
used to combine or aggregate IMG metadata for some IMG receivers. An
IMG receiver may be allowed to receive IMG metadata from any number
of IMG senders.
IMG metadata is used to find, obtain, manage and play content. IMG
metadata distributions may be modified as they are distributed. For
example, a server may use IMGs to retrieve media content via unicast
and then make it available at scheduled times via multicast, thus
requiring a change of the corresponding metadata. IMG transceivers
may add or delete information or aggregate IMG metadata from
different IMG senders. For example, a rating service may add its own
content ratings or recommendations to existing metadata. An
implication of changing (or aggregating) IMG metadata from one or
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representing session-level parameters of IMG metadata. Compared to
SDP, the XML-based format of SDPng should be much more flexible with
regards to extensions and combining with other description formats.
MPEG-7: Descriptions based on the MPEG-7 standard could provide
application-specific metadata describing the properties of multimedia
content beyond parameters carried in SDP or SDPng descriptions.
MPEG-7 provides a machine-readable format of representing content
categories and attributes, helping end-users or receiving software in
choosing content for reception: this is well in line with the IMG
usage scenarios of IMGs introduced in 3.2. MPEG-7 is based on XML so
it is well suited for combining with other XML-based formats such as
SDPng.
TV-Anytime Forum: The TV-Anytime Forum [5] provides descriptions
based on XML schema for TV-specific program guides. TV-Anytime uses
the MPEG-7 User description profile to a limited extent (for user
preferences and usage history) and also a TV-Anytime-specific data
model for other schema - which are optimised to describe broadcast
schedules, on-demand program guides and program events.
HTTP: The HTTP protocol can be used as a bi-directional/unicast IMG
transport protocol. Being a request-reply oriented protocol, HTTP is
well suited for implementing synchronous operations such as QUERY,
RESOLVE and even SUBSCRIBE. However, HTTP does not provide
asynchronous operations such as ANNOUNCE and NOTIFY and to implement
asynchronous operations using HTTP, IMG receivers should poll the IMG
sender periodically. So alone, HTTP is not sufficient to fulfill IMG
requirements in a unicast deployment.
SAP: The announcement mechanism provided by SAP provides
unidirectional delivery of session discovery information. Although
SDP is the default payload format of SAP, the use of a MIME type
identifier for the payload allows arbitrary payload formats to be
used in SAP messages. Thus, SAP could be used to implement the
(multicast and unicast) IMG ANNOUNCE and IMG NOTIFY operations.
However, the limitations of SAP as a generic IMG transport protocol
include:
- Lack of reliability (through forward error correction /
retransmissions)
- Lack of payload segmentation
- Limited payload size
- Only one description allowed per SAP message
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- Lack of congestion control
- Lack of Internet standard authentication / encryption mechanisms
- It is an Experimental RFC with no support for progressing further
In principle, the current SAP protocol could be extended to get
around its limitations (e.g. the use of a multipart MIME type in the
SAP payload enabling multiple descriptions to be carried in a single
SAP message). However, the amount of changes needed in SAP to address
all of the above limitations would effectively result in a new
protocol. Due to these limitations, the use of SAP as an IMG
transport protocol is not recommended.
SIP: The SIP-specific event mechanism described in RFC 3265 [6]
provides a way to implement IMG SUBSCRIBE and IMG NOTIFY operations
via a bi-directional unicast connection. However, there are
scalability problems with this approach, as RFC 3265 currently does
not consider multicast.
RTSP: The RTSP protocol defines a retrieval and update notification
mechanism, named DESCRIBE and ANNOUNCE, for the description of a
presentation or media object in order to initialize a streaming
session. These methods are subset of the entire streaming control
operations in RTSP, thus these could not be available for individual
mechanisms. However, the DESCRIBE method in RTSP could be use to
instantiate IMG QUERY, IMG RESOLVE and IMG SUBSCRIBE, and the RTSP
ANNOUNCE could be use to instantiate an IMG NOTIFY for a streaming
session controlled by RTSP.
5.2 Outstanding IMG Mechanism Needs
Several outstanding needs result from the IMG requirements, framework
model and existing relevant mechanisms as already shown in this
document. Four specific groupings of work are readily apparent which
are: (a) specification of an adequate multicast and unidirectional
capable announcement protocol; (b) specification of the use of
existing unicast protocols to enable unicast subscribe and
announcement/notification functionality; (c) specification of the
metadata envelope which is common to, and independent of, the
application metadata syntax(es) used; (d) agreement on basic metadata
models to enable interoperability testing of the above. The following
sections describe each of these.
5.2.1 A Multicast Transport Protocol
SAP is currently the only open standard protocol suited to the
unidirectional/multicast delivery of IMG metadata. As discussed, it
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fails to meet the IMG requirements in many ways and, since it is not
designed to be extensible, we recognize that a new multicast
transport protocol for announcements needs to be specified to meet
IMG needs. This protocol will be essential to IMG delivery for
unidirectional and multicast deployments.
The Asynchronous Layered Coding (ALC) [7] protocol from the IETF
Reliable Multicast Transport (RMT) working group is very interesting
as it fulfils many of the requirements, is extensible and has the
ability to 'plug-in' both FEC (Forward Error Correction -- for
reliability) and CC (Congestion Control) functional blocks -- it is
specifically designed for unidirectional multicast object transport.
ALC is not fully specified, although RMT has a fully specified
protocol using ALC called FLUTE (File Delivery over Unidirectional
Transport) [8]. FLUTE seems to be the only fully specified transport
and open specification on which a new IMG announcement protocol could
be designed. Thus we recommend that ALC and FLUTE be the starting
points for this protocol's design.
Developing a new protocol from scratch, or attempting to improve SAP,
is also feasible, although it would involve repeating many of the
design processes and decisions already made by the IETF for ALC.
Thus, we recommend only to attempt this if ALC-based protocols are
later found to be insufficient.
In particular, any announcement protocol must feature sufficient
scalability, flexibility and reliability to meet IMG needs. Also, the
IMG ANNOUNCE operation must be supported and IMG NOTIFY capability
could be investigated for both hybrid unicast-multicast and
unidirectional unicast systems.
5.2.2 Usage of Unicast Transport Protocols
A thorough description of the use of existing unicast protocols is
essential for the use of IMGs in a unicast point-to-point
environment. Such a specification does not currently exist, although
several usable unicast transport protocols and specifications can be
harnessed for this (SIP [9], SIP events [6], HTTP [10], etc.) In
particular, both IMG SUBSCRIBE-NOTIFY and IMG QUERY-RESOLVE operation
pairs must be enabled. We anticipate that the IMG QUERY-RESOLVE
operation will be a trivial usage of HTTP, although other transport
protocol options may be beneficial to consider too.
5.2.3 IMG EnvelopeSection 3.2.6 of this document discussed the need for binding between
IMG Operations and Data Types. Such a binding can be realized by
defining a common minimal set of information needed to manage IMG
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metadata transfers, and by including this information with any set of
IMG metadata delivered to IMG receiver(s).
Four options for IMG metadata transfer envelope delivery are
feasible:
1. Embedding in a transport protocol header. This can be done
with either header extensions of existing protocols, or
newly defined header fields of a new (or new version of a)
transport protocol. However, multiple methods for the
variety of transport protocols would hinder
interoperability and transport protocol independence.
2. A separate envelope object, which points to the IMG
metadata 'object', delivered in-band with the metadata
transport protocol session. This might complicate
delivery as the envelope and 'service' metadata objects
would have to be bound, e.g. by pairing some kind of
transport object numbers (analogous to port number pairs
sometimes used for RTP and RTCP [11]). This would also
enable schemes which deliver enveope and metadata
'objects' on by different media, also using more than a
single transport protocol.
3. A metadata wrapper which points to and/or embeds the
service metadata into its 'super-syntax'. For example, an
XML would enable embedding generic text objects.
4. Embedding in the metadata itself. However, this requires
new field in many metadata syntaxes and would not be
feasible if a useful syntax were not capable of
extensibility in this way. It also introduces a larger
'implementation interpretation' variety which would hinder
interoperability. Thus this option is not recommended.
It is likely that more than one of these options will fulfill the
needs of IMGs so the selection, and possibly optimization, is left
for subsequent specification and feedback from implementation
experience. Such a specification is essential for IMG delivery.
When there are superset/subset relations between IMG descriptions,
it is assumed that the IMG descriptions of the subset inherit the
parameters of the superset. Thus, an IMG metadata transfer envelope
carrying the IMG descriptions of a superset may implicitly define
parameters of IMG descriptors belonging to its subset. The
relations between IMG descriptions may span from one envelope to
another according to a data model definition.
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Internet Draft IMG Framework June 21, 2004
A minimal IMG data model may be useful to any implementer/deployment
of IMGs. The purpose would be to ensure that multiple metadata
syntaxes (SDP, MPEG-7, etc.) can be related within the same body of
IMG knowledge, regardless of any specific metadata and data models
provided by the metadata syntaxes.
Further work may be needed to meet application-specific requirements
at defining metadata and data models for the successful deployment of
IMGs in various environments. Existing (and future) work on these
would need to be mapped to the IMG data types and use of the IMG
transfer envelope concept as described above.
This document is a framework for the delivery of IMG metadata and
thus further discussion on the definition data models for IMGs is
beyond its scope.
5.3 IMG Needs Fitting the IETF's Scope
A multicast transport protocol is essential to IMG delivery for
unidirectional and multicast deployments and no alternative exists
which fulfils the IMG requirements. We recommend that the
specification of this be taken on as an official work item in the
IETF.
Specification of the usage of unicast transport protocols is
essential for IMG delivery and control involving unicast
communications, and will relate to existing IETF standard transport
protocols. Thus, we recommend that the specification of this be taken
on as an official work item in the IETF.
The IMG metadata transfer envelope functionality is essential for the
IMG delivery fulfilling the IMG requirements. It is a required
feature for IMG metadata transport and maintenance. Thus, we
recommend that the IMG transfer envelope specification be taken on as
an official work item in the IETF.
(Meta)data model specification and application specific metadata do
not easily fit into the IETF scope and several other standardization
bodies are well placed to do this work. This aspect need not be an
official IETF work item.
Note, we acknowledge the need to exchange and agree on a baseline
metadata model and application specific metadata for the purposes of
interoperability testing between different implementations of IMG
related IETF protocols. However, we feel that the IETF standards
process may not be required for this.
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The IMG framework is developed from the IMG requirements document [4]
and so the selection of specific protocols and mechanism for use with
the IMG framework must also take into account the security
considerations of the IMG requirements document. This framework
document does not mandate the use of specific protocols. However, an
IMG specification would inherit the security considerations of
specific protocols used, although this is outside the scope of this
document.
Protocol instantiations which are used to provide IMG operations will
have very different security considerations depending on their scope
and purpose. However, there are several general issues which are
valuable to consider and, in some cases, provide technical solutions
to deal with. These are described below.
Individual and Group Privacy: Customized IMG metadata may reveal
information about the habits and preferences of a user and may thus
deserve confidentiality protection, even if the original information
were public. Snooping and protecting this IMG metadata requires the
same actions and measures as for other point-to-point and multicast
Internet communications. Naturally, the risk of snooping depends on
the amount of individual or group personalization the snooped IMG
metadata contains. Further consideration is valuable at network,
transport and metadata levels.
IMG Authenticity: In some cases, the IMG receiver needs to be assured
of the origin of IMG metadata or its modification history. This can
prevent denial of service or hijacking attempts which give an IMG
receiver incorrect information in or about the metadata, thus
preventing successful access of the media or directing the IMG
receiver to the incorrect media possibly with tasteless material.
Action upon detection of unauthorized data insertion is out of scope
of this document.
IMG Receiver Authorization: Some or all of any IMG sender's metadata
may be private or valuable enough to allow access to only certain IMG
receivers and thus make it worth authenticating users. Encrypting the
data is also a reasonable step, especially where group communications
methods results in unavoidable snooping opportunities for
unauthorized nodes. Encryption and the required security parameters
exchange are outside the scope of this document.
Unidirectional Specifics: A difficulty that is faced by
unidirectional delivery operations is that many protocols providing
application-level security are based on bi-directional
communications. The application of these security protocols in case
of strictly unidirectional links is not considered in the present
document.
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Malicious Code: Currently, IMGs are not envisaged to deliver
executable code at any stage. However, as some IMG transport
protocols may be capable of delivering arbitrary files, it is
RECOMMENDED that the IMG transport methods do not have write access
to the system or any other critical areas.
Protocol Specific Attacks: It is recommended that developers of any
IMG protocol take account of the above risks in addition to any
protocol design and deployment environment risks that may be
reasonably identified. Currently this framework document does not
mandate the use of any specific protocols, however the deployment of
IMGs using specific protocol instantiations will naturally be subject
to the security considerations of those protocols.
Security Improvement Opportunity: The security properties of one
channel and protocol can be improved through the use of another
channel and protocol. For example, a secure unicast channel can be
used to deliver the keys and initialization vectors for an encryption
algorithm used on a multicast channel. The exploitation of this
opportunity is specific to the protocols used and is outside the
scope of this document.
7 IANA Considerations
There are no IANA considerations within this document.
8 Normative References
[1] S. Bradner, "Key words for use in RFCs to indicate requirement
levels," RFC 2119, Internet Engineering Task Force, Mar. 1997.
9 Informative References
[2] M. Handley and V. Jacobson, "SDP: session description protocol,"
RFC 2327, Internet Engineering Task Force, Apr. 1998.
[3] D. Kutscher, J. Ott, and C. Bormann, "Session description and
capability negotiation," Internet Draft draft-ietf-mmusic-sdpng-07,
Internet Engineering Task Force, Oct. 2003. Work in progress.
[4] Y. Nomura, R. Walsh, J-P. Luoma, J. Ott, and H. Schulzrinne,
"Requirements for Internet Media Guides," Internet Draft
draft-ietf-mmusic-img-req-07, Internet Engineering Task Force, June
2004. Work in progress.
[5] TV-Anytime Forum, "Broadcast and On-line Services: Search,
select, and rightful use of content on personal storage systems
("TV-Anytime Phase 1"); Part 2: System description," ETSI-TS 102
822-2: System Description, V1.1.1, October 2003.
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Internet Draft IMG Framework June 21, 2004
Finland
Email: juha-pekka.luoma@nokia.com
Hitoshi Asaeda
INRIA
Project PLANETE
2004, Route des Lucioles, BP93,
06902 Sophia Antipolis,
France
Email: Hitoshi.Asaeda@sophia.inria.fr
Henning Schulzrinne
Dept. of Computer Science
Columbia University
1214 Amsterdam Avenue
New York, NY 10027
USA
Email: schulzrinne@cs.columbia.edu
12 Full Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78 and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
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Internet Draft IMG Framework June 21, 2004
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
Y. Nomura et. al. [Page 24]